1. Field of the Invention
The present invention relates to an image forming apparatus, such as a printer, a copier, a facsimile, etc., capable of temporarily capturing toner adhering to a surface of an image bearer into a blush after a transfer step, and capable of returning the toner to the surface of the image bearer from the blush at a prescribed time.
2. Discussion of the Background Art
In a conventional image forming apparatus that employs an electro-photographic system, an image is formed in a process as described below. That is, exposure scanning is applied to an image bearer, such as a photoconductive member, etc., uniformly charged by a charging apparatus with electricity, and a latent image is formed thereon. A developing apparatus then develops the latent image. A toner image thus obtained by development is transferred from the image bearer to a printing member such as a printing sheet either directly or via an intermediate transfer member. In such a process, toner not transferred either onto the printing member or the intermediate transfer member adheres to the surface of the image bearer as post transfer toner after the transfer process is completed. A cleaning recycle mechanism is then sometimes employed to remove the post transfer toner from the image bearer using a cleaning blade, and conveys the toner to the developing apparatus to recycle the same.
However, since this type of a cleaning recycle mechanism necessitates a toner conveyance mechanism for conveying the post transfer toner scraped from the surface of the image bearer to the developing apparatus, the image forming apparatus becomes complicated and balky.
As an image forming apparatus capable of handling post transfer toner without a cleaning recycle mechanism, a technology of temporarily capturing post transfer toner with a blush member is known as described in Japanese Patent Application Laid Open No. 2004-170530. This type of image forming apparatus executes a temporary capturing process capable of temporally capturing post transfer toner scraped off from the surface of the image bearer with a blush member. Then, the image forming apparatus executes a returning process for returning the toner from the brush to the surface of the image bearer while changing a bias condition at a prescribed time such as when a print job is completed. Then, by transferring the toner into a developer carrier such as a developing roller arranged in a developing apparatus from the surface of the image bearer, the post transfer toner is finally collected within the developing apparatus. Since a complicated toner transfer mechanism such as a conveyance screw, a conveyance belt, etc., is not needed in such a configuration, the image forming apparatus can be downsized at low cost.
However, in this type of image forming apparatus, toner is gradually accumulated in the brush as long time elapses. As a result, an abnormal image is sometimes created. Specifically, toner scraped off from the surface of the image bearer by a brush having a plurality of raisings is taken in between raisings in the brush. Specifically, almost all of the toner taken in generally stays at a tip of the brush, and then smoothly returns to the surface of the image bearer in a returning process. However, there exists some toner deeply entering the brush owing to the influence of behavior of the brush after being taken in the brush.
Such toner can't smoothly move to the tip of the brush for the below-described reasons. Specifically, in the returning process, an electric flux line created at a contact section between the brush and the image bearer extends almost straight along a vertical line in relation to the surface of the image bearer. In contrast, the raising contacting the surface of the image bearer is bent following the moving surface of the image bearer. The toner deeply staying in the brush between the raisings collide with a side surface of the raising bending in a direction when moving straight along the electric flux line. Thus, the toner can't smoothly move to the tip.
For the above-mentioned reasons, toner is gradually accumulated on the root side of the brush as time elapses. Later on, an abnormal image is created for variety of causes.
For example, when a brush member is used to double as a charging member for uniformly charging the surface of the image bearer, the toner accumulated in the brush makes discharge unstable between the brush and the image bearer, thereby creating uneven charge. As a result, an abnormal image such as uneven density is created.
When a lot of toner is accumulated in the brush, the mass of toner is inversely transferred back to the image bearer in a block even though temporal capturing is on the way due to influence of the behavior of the brush. Then, the toner prevent uniform discharging of an image bearer during a later exposure step, thereby, uneven discharge or write error is caused on the image bearer in the latent image writing step.